1. Field of the Invention
The present invention relates generally to power conservation in a battery operated, microprocessor based system, and more particularly, toward a battery conserving circuit, wherein battery power to a microprocessor is strobed to save power and wherein the off-time of the stroke is controlled by a timer external to the microprocessor.
2. Description of the Prior Art
Non-microprocessor controlled systems have been used for monitoring parameters at a plurality of remote points, and a remote monitoring station containing external condition responsive sensors is located at each point. The sensors are designed to detect various parameters of interest. For example, in a security system, the sensors may be responsive to open or close doors, windows or the like; and in other control systems, to the condition, for example, of a group of thermostats. It appears desirable that each remote station should contain a microprocessor that monitors the sensors, stores electrical signals developed by the sensors, and transmits the signal to a central console during polling; but such use of microprocessors has not been economically feasible.
The term "microprocessor" (.mu.p) as referred to herein is considered to be a central processing unit having an internal clock, preferably fabricated on a single chip, and powered from a single power supply terminal. The .mu.p typically includes an arithmetic and logic unit (ALU), an input/output state and control stages.
When a remote station uses a microprocessor it may be operated by commercial line power through an appropriate power supply converter and there is no economic problem. In some applications, such as security monitoring, it is mandatory that each remote station remain operative at all times. In the event of a power line failure, for example, a back-up battery is generally provided that automatically is switched into the power supply circuit in place of the power supply converter. Upon return of line power, the battery is automatically switched out of circuit and simultaneously replaced by the power supply converter.
The back-up battery systems in the prior art of which I am aware have been generally satisfactory for short term power failures. Since a microprocessor draws a substantial amount of current, however, the back-up battery becomes fully discharged in a relatively short period of time, and its use is not economically feasible for long periods of time. It has been estimated, for example, that a typical back-up battery has a capacity of about 8 hours of continuous operation under load by a standard microprocessor. In security monitoring systems, however, 8 hours of back-up operation is unsatisfactory; back-up operation of at least 80 hours may be necessary during a line power failure in a vacated facility over a three day weekend, for example, wherein the failure may be unnoticed or unrepairable.
Accordingly, one object of the present invention is to provide a circuit for conserving battery consumption in a battery operated, microprocessor based system.
Another object is to provide a circuit for strobing battery power to a microprocessor at predetermined times in order to minimize battery consumption.
Another object is to provide a circuit that strobes battery power to a microprocessor under program control, wherein the microprocessor is connected to the battery only during task performance and is disconnected from the battery at all other times.
In prior art of which I am aware, memory stages have been strobed by a battery only during periods of time that the memories are being written into or read out. In other prior art, data processing circuitry is continuously energized while a display module is periodically deenergized to conserve battery power. In still other prior art, various sections of data processing system are successively energized by a battery while remaining sections are deenergized, with all sections eventually being energized for various time durations. None of the prior art systems of which I am aware, however, provides any means for strobing battery power to a microprocessor and doing so by transferring power-return control to an external timer and switch during the power-off time periods. In other words, all prior systems of which I am aware, keep the "intelligent controller" (microprocessor) active all of the time; whereas an object of the invention involves turning off the intelligent controller and allowing a very simple (and low current) unintelligent circuit to turn it back on.
Another object of the invention, therefore, is to provide a battery saving circuit in a microprocessor based system, wherein the microprocessor is deenergized upon completion of a programmed task and re-energized under control of an external control means for performance of another programmed task.
Another object is to provide a battery saving circuit in a microprocessor based system, wherein the power connection between a battery and a microprocessor is interrupted under control of the microprocessor upon completion of a programmed task, an external timer is simultaneously triggered by the microprocessor to time out a predetermined or programmed time period, and wherein the external timer reestablishes the power connection after the predetermined time period to energize the microprocessor for performance of another programmed task.